From: Steinar H. Gunderson <steinar+git@gunderson.no>
Date: Tue, 6 Oct 2020 20:20:00 +0000 (+0200)
Subject: Hand-roll zeroing of destination docids for SSE2; takes us seemingly up from ~84... 
X-Git-Tag: 1.0.0~42
X-Git-Url: https://git.sesse.net/?a=commitdiff_plain;h=0bf819d19af7ae0f5b7255322658f5aaa2b14192;p=plocate

Hand-roll zeroing of destination docids for SSE2; takes us seemingly up from ~84% to ~89% of reference.
---

diff --git a/turbopfor.h b/turbopfor.h
index e4c31e6..84e354d 100644
--- a/turbopfor.h
+++ b/turbopfor.h
@@ -507,7 +507,11 @@ const unsigned char *decode_pfor_bitmap_interleaved_128_32(const unsigned char *
 	constexpr unsigned BlockSize = 128;
 	using Docid = uint32_t;
 
-	memset(out, 0, BlockSize * sizeof(Docid));
+	// Set all output values to zero, before the exceptions are filled in.
+	#pragma GCC unroll 4
+	for (unsigned i = 0; i < BlockSize / 4; ++i) {
+		_mm_storeu_si128(reinterpret_cast<__m128i *>(out) + i, _mm_setzero_si128());
+	}
 
 	const unsigned bit_width = *in++ & 0x3f;